1. Field of the Invention
The present invention generally relates to fixtures for holding workpieces during lapping and polishing operations and more specifically to an improved fixture which accommodates different sized workpieces.
2. Description of the Related Art
Ceramic substrates routinely go through a process of lapping and/or polishing, after they have been fired, to achieve desired flatness, roughness and thickness specifications. These processes involve the fixturing of the substrate in a dressing wheel or polishing head which is then turned on a spinning table upon which abrasive slurries are applied.
FIG. 1 illustrates a conventional double-sided lapping machine. Motor 1 turns gearbox 2 to drive an upper dressing/working wheel 3. Similarly, motor 8 turns gear box 9 to drive a lower dressing/working wheel 7, via a belt 10. A workpiece to be lapped (not illustrated) is placed in a fixture (not illustrated), between two working wheels 3 and 7. Motor 4 and belt 6 turn gear box 5 to drive a workpiece drive 11.
A large wheel 20 (shown in FIG. 2), typically made of spring-steel that contains round openings 21, is mounted on the workpiece drive 11. The workpiece drive 11 turns the large wheel 20. Plastic fixtures 22 (e.g., disks) are inserted into these round openings 21. It is these fixtures 22 that are the subject of this invention.
FIG. 3 shows a conventional fixture 30 that holds two ceramic substrates 40 (FIG. 4) for lapping or polishing in separate openings 31. The fixture 30 holds the substrate 40 in place and must be fabricated to fit the individual substrates 40. The fixture 30 can be made of any machinable material, such as polyvinyl chloride (PVC), plastic or metal.
The fixture 30 must be thinner than the workpiece or substrate 40 and thin enough to allow for sufficient removal of material from the workpiece 40. Openings 31 are typically fabricated to a tolerance of xe2x88x920.000xe2x80x3/+0.005xe2x80x3 of the overall length 41 and width 42 of the workpiece 40 to be lapped or polished. This tolerance is required to minimize the amount of movement within the opening 31. Too much movement results in chipping of the workpiece edges during lapping and polishing.
If the opening 31 in the fixture 30 is too small, the substrate 40 will not fit inside the fixture 30. If the opening 31 in the fixture 30 is too big, the substrate 40 will move around too much and will result in xe2x80x9cchippingxe2x80x9d on the substrate.
This invention solves the problem that occurs when the length 41 and width 42 of the substrate 40 varies more than the tolerance of the fixtures 30. This usually occurs when the workpiece 40 is to be lapped and/or polished after sintering. In other words, the length 41 and/or the width 42 of the workpiece 40 commonly varies by more than 0.005xe2x80x3.
Conventional solutions to this problem include a sizing operation between sintering and lapping or polishing. In this manner, all parts (e.g., substrates 40) would be accurately cut to fit the opening 31. However, this is an expensive solution. Another conventional solution is making multiple sized openings 31 and xe2x80x9cbest fittingxe2x80x9d the parts 40 to the openings 31. However, this process is time consuming and difficult.
It is, therefore, an object of the present invention to provide a structure and method for the fabrication of curved flexures built into the fixture that maintain contact with the workpiece at all times. Any movement within the fixture will be dampened by the flexure.
The flexures can be adjusted for different dampening strengths. The flexures can also provide a single contact point with the workpiece sides or multiple contact points. The flexures can be fabricated using typical machining or punching methods.
More specifically, the invention includes a fixture for holding a workpiece in a polishing/lapping apparatus. The fixture comprises at least one opening having at least one curved flexible side for elastically holding the workpiece and a slot adjacent each curved flexible side for allowing the side to flex.
The slot has a length approximately equal to that of the side and a shape approximately equal to that of the side. An amount of travel of the side is controlled by a width of the slot.
The invention also includes a web positioned between the side and the slot, wherein a tension of the side against the workpiece is controlled by a width of the web.
The side is curved toward a center of the opening such that the workpiece contacts the side only at a distinct point. The side can also be a multiple-curve side having at least two curves, such that one distinct point on each curve of the at least two curves touches a same side of the workpiece. The opening can be a four-sided opening having a first number of the curved flexible sides and a remaining number of straight sides. The fixture can comprise one of a plastic, polyvinyl chloride, metal or other suitable material.
The invention similarly includes an apparatus for machining a workpiece, the apparatus comprising a motor, a wheel turned by the motor, a fixture attached to the wheel and for holding a workpiece in the machining apparatus. The fixture comprises at least one opening having at least one curved flexible side for elastically holding the workpiece.
The invention also includes a method for producing a fixture for holding a workpiece in a machining apparatus, comprising steps of supplying a disk of material, forming at least one opening in the disk of material having at least one curved flexible side for elastically holding the workpiece. The invention similarly includes a method of machining a workpiece comprising forming a fixture for holding the workpiece in a machining apparatus, forming at least one opening in the fixture having at least one curved flexible side for elastically holding the workpiece, mounting the workpiece in the opening, elastically holding the workpiece, using the curved flexible side, in the opening and machining the workpiece while being held by the fixture.